A lenticular screen or sheet is commonly used to separate left and right images in a 3D picture or a 3D display. As shown in FIG. 1, a lenticular sheet 10 has a plurality of cylindrical lenses known as lenticules 20. At the base of each lenticule 20, at least two compressed images 30 are provided such that when a viewer views the 3D print, the left eye (LE) can see the left compressed images (LI) and the right eye (RE) can see the right compressed images (RI). If the compressed images (LI) and the compressed images (RI) are the images of the same scene taken at two different angles, the viewer would see a 3D image of the scene. It should be noted that, in some print with a lenticular sheet 10, the compressed images (LI) and the compressed images (RI) may be images that are not related to each other. For example, the printed images can be an image of an orange and an image of an apple. For that reason, the print 35 composed of the compressed images 30 is referred herein as a composite print.
In a 3D print or a composite print, each of the lenticules 20 is a parallax separator. Its main function is to limit the viewing angle within which a certain part of the compressed images can be seen at a certain angle. A lenticular sheet 10 is effectively a parallax barrier. FIG. 2A is a schematic presentation showing how the compressed images are produced. As shown in FIG. 2A, a left image 55L and a right image 55R are displayed, presented or projected at an object plane, one or more projection lenses 40 are used to projected the left image 55L and the right image 55R onto an image plane at different angles. When the projected images fall on the lenticular sheet 10, each of the lenticules 20, relying on the compression characteristics of a cylindrical lens, directs a portion of the projected left image to the left half of the lenticule base to form the compressed image LI and directs a portion of the projected right image to the right half of the lenticule base to form the compressed image RI. FIG. 2B is a schematic presentation showing the projection of a pair of images 50L, 50R with a width W through a lenticular sheet 10 having N lenticules 20 to produce a composite print 35. In general, the lenticular sheet 10 covering the composite print 35 has hundreds or thousands of lenticules 20, depending on the size of the composite print 35 and the pitch of the lenticular sheet 10. For simplicity, let us assume N=5, a non-realistically small number. As such, the composite print 35 is composed of five pairs of compressed image components (a1, b1), (a2, b2), (a3, b3), (a4, b4) and (a5, b5). Since an image having a width W is projected onto N lenticules, the compressed image component in each lenticule is corresponding to a portion (W/N) of the image. Thus, if we divide the image 55L into N (=5) parts: A1, A2, A3, A4 and A5, the compressed image a1 is corresponding to the image portion A1, the compressed image a2 is corresponding to the image portion A2, etc. Likewise, the compressed image b1 is corresponding to the image portion B1, etc.
In the above illustration, a composite print is composed of N pairs of compressed images, produced from two images 55L and 55R. A composite print can also be produced from three or more images as shown in FIG. 2C. In FIG. 2C, three images 55L, 55C, 55R are projected by projection lens onto a lenticular sheet 10 to make a composite image 35 such that each lenticule 20 has three compressed image components RI, CI and LI.